Venous occlusion plethysmography versus Doppler ultrasound in the assessment of leg blood flow during calf exercise

This study explored the accuracy with which venous occlusion plethysmography (VOP) assesses the hyperaemic response during calf exercise. Using Doppler ultrasound (DU) as a criterion standard technique, we tested the hypotheses that leg blood flow during contraction is not greater than at rest and that VOP provides similar estimates of the hyperaemic response between contractions as DU. Eleven subjects performed several bouts of calf exercise across a wide range of forces (50–400 N ≅ 6–45%MVC). Each bout consisted of 2 min of intermittent contractions preceded and immediately followed by sustained (40 s) contractions. DU estimates of leg blood flow during the sustained contractions were never significantly greater (P > 0.05) than those measured at rest. Paired (DU and VOP) estimates of leg blood flow (n = 488) were obtained between intermittent contractions and ranged between ~50–900 ml min⁻¹. There was a strong correlation between these DU and VOP estimates (Pearson r = 0.91; P < 0.05). Ordinary least products regression analysis, with VOP as the y variable, showed a relatively small proportional bias (slope = 0.942; CI = 0.938–0.946) and fixed bias (y intercept = −13.3 ml min⁻¹; CI = −14.4 to −12.2 ml min⁻¹) between the two measurement techniques. Since these small biases can be explained by the slight differences in vascular regions which the two techniques assess, these data suggest that VOP can accurately assess the hyperaemic response to exercise.